HANDS on Position Sensor Introduction to ANSYS Maxwell PRACE 2013

2013 CADFEM GmbH Seite 1

Position Sensor-Simulation

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ANSYS Maxwell 3D (Hands-On Notes)

Topics: Introduction into Maxwell for static magnetic field simulation


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Table of Contents

1 Position Sensor-Simulation ............................................................................................................................. 4

1.1 Introduction ............................................................................................................................................. 4

1.2 Initial Setup ............................................................................................................................................. 5

1.3 Setting up Sensor Simulation .................................................................................................................. 6

1.4 Sensor Parameter Setup ......................................................................................................................... 16

1.5 Insert Parametric Rotation of the Wheel .............................................................................................. 19

1.6 Workbench Parametric Run .................................................................................................................. 20


1 Position Sensor Simulation

1.1 Introduction

The correct measurement of an angular position (or speed) is required in many different applications. One of

the typical realization principle is based on the evaluation of the magnetic field quantities which are effected by

moveable (rotating) permeable region nearby. Many of such applications are using a difference signal of 2 field

sensors(e.g. Hall or MR elements) to measure the H-Field showing reluctance effects (for static methods) or

eddy effects (for dynamic effects).

A well known application of such a principle using MR-elements is shown in figure 1. Here cylindrical

permanent magnet works as a field source for the 2 sensor elements and the structured rotating wheel.

Figure 1

While the field source remains constant, the magnetic resistance depends on the angular position of the

structured wheel.


Figure 2 gives a more detailed picture of the region of interest (sensor region). As the size of the sensors is

significantly small compared to the wheel, the simulation needs to evaluate the field distribution with care.

Figure 2

The goal of the simulation is to determine the field quantities with respect to the angular position of the wheel.

In some further optimization runs the difference signal should be optimized, while the magnet size should be

minimized.

1.2 First Steps (initial Settings of Workbench)

Open ANSYS Workbench

Set the Language to English: Tools > Options > Regional and Language Options > Language > English

Close ANSYS Workbench, that the language changes become active

Open ANSYS Workbench again.


1.3 Setting up Sensor Simulation

Insert a new Maxwell3D Simulation (from analysis systems inside the project page)

Open Maxwell3D (double-click onto the analysis system) The figure shows the GUI of ANSYS Maxwell:

Figure 3

Modeling Setup

Import the Geometrie (Parasolid): Modeler > Import > SENSOR_GEOM.x_t

Figure 4


Save the Workbench Project: File > Save As > SENSOR_GEOM.x_t.wbpj

Open the Maxwell3D component system

Assign Material Properties to all Solid Parts:

Point onto the Magnet (inside Solid Tree or within graphics window)

Use RMB to choose Assign Material

Figure 5

Insert NdFE into the material name box to search for existing data sets

Accept the material with OK


You may check the content of the material data (from Library) as well as adjust settings with the View/Edit

function. Here you can see that the magnetization direction is oriented as global X direction. This setting is

correct for our analysis here.

Proceed similar for the other solids, to point vacuum to the sensors (the are non magnetic regions) , as well as

the region. Choose Iron from the library to point onto the wheel. For the first analysis the linear description of

iron is suitable here.

The graphics properties can also be adjusted for each solid. You may use the Properties Window (left side under

the tree) to adjust colors and transparency. Moreover also the use of the solid within the simulation can by

specified (Model or Non-Model).

Figure 6


As the next step, the boundary condition should be set. Thus its helpful to rotate the model. This can be done

with the middle mouse button, while the scroll-wheel helps for zooming in and out.

Assume the field at the end regions of the sector of the wheel are not effected by the magnet a flux parallel

boundary condition (natural) is sufficient for the basic setup.

The definition of initial mesh parameters help to improve the performance and accuracy. For this step a sizing

for the sensor region is required.

Select the Sensor Solids

Use RMB to choose Apply Mesh Operation > Inside Selection > Length based

Figure 7

Specify 0.02 mm

Proceed similar to define 1mm for the magnet and 3 mm for the wheel.


As the basic setup is nearly finished the analysis setup can be implemented:

RMB in Analysis > Add Solution Setup

Figure 8

The original setup shows 10 adaptive iterations to fulfil the energy criteria (global)

Figure 9


The validation checking can be used to validate of all requirements for the analysis are fulfilled.

Use the appropriate function from the main menu.

Figure 10

Next the analysis can be started.

Figure 11


The simulation progress can be seen on the main screen showing also the adaptive iterations.

Figure 12

The convergence can be check with:

RMB Analysis Setup1> Convergence

Figure 13


To proceed with some further steps, it may be helpful to hide the field region. This can be done with the eye

filters in the main menu.

Figure 14

Resulting to the picture of figure 15.

Figure 15


Insert a field-plot to display the magnetic field of the wheel.

Select the solid body of the wheel

Use RMB to choose Fields > H> Mag_H

Figure 16

Check the Box on surface only to create a contour plot

Figure 17


The resulting field plot should look like figure 18. The field is concentrated to the region near to the magnet

and will be symmetric, as the initial position with respect to the structure of the wheel is also symmetric.

Figure 18


1.4 Sensor Parameter Setup (Calculator)

As the sensor signal is derived from the magnetic field in the region of the sensor domain, the field calculator

of Maxwell will be used to determine this data.

Select Field Overlays (in tree) > RMB Calculator

Figure 19


The equation in figure 20 shows the relation that should be evaluated with the field calculator for both sensors:

Figure 20

For the Forward Sensor (FWD)

Qty H Scalar Y

Geom Sens_Fwd Integ

Qty H Scalar X

Geom Sens_Fwd Integ

/

Trig Atan

Constant PI /

Number 180.0 *

[Add] Ang_Fwd

And also for the Backward Sensor (Back)

Qty H Scalar Y

Geom Sens_Back Integ

Qty H Scalar X

Geom Sens_Back Integ

/

Trig Atan

Constant PI /

Number 180.0 *

[Add] Ang_Back

Finish with DONE.


The evaluated quantities can be displayed with:

Results RMB> create field report > Data table

Choose from the calculator expression ANG_BACK and ANG_FWD

New report

Figure 21

Insert these variables as convergence criteria:

RMB Analysis Setup 1 > Properties > Expression Cache > Add

ADD the ANG_BACK and ANG_FWD

Done

Adjust the convergence to 0.05 for each parameter

Figure 22

The next analysis run will also consider this definition.


1.5 Insert Parametric Rotation of the Wheel

As the sensor detects the field quantities as a function of the angular position of the wheel, a rotation of the

geometry is inserted:

Select the Wheel and Region !

RMB > Edit > Arrange > Rotate > type angle into the data field to rotate about z

Figure 23

The program will ask for the value of the new defined parameter angle:

Figure 24

Type an initial value of 0 into the field and finish with ok. The parameter could be found and adjusted in details

window (properties) of the Maxwell3DDesign.

This can also be used to check the operation with different values.


1.6 Workbench Parametric Run

To evaluate the function of the field values (for the sensor) relating to the position the Workbench Parameter

Run can be used (in combination with other physics or the optimization tool OptiSlang)

Choose Optimetrics > DefaultDesignXplorerSetup

RMB properties > check include to the variable angle

Choose Calculation Tab > Add Expression Cache for Ang_FWD and Ang_BWD

Done and OK

Save the Simulation Setup within Maxwell (Crtl+S). This will link the Maxwell parameters into WB.

Figure 25

Now the parameter sets can be defined and the parametrized analysis could be started:

Double-Klick onto the Parameter Set

Type a new value into the empty field under the existing angle (line2 = current design)

Proceed to define values from -7.5 to 7.5

Use Update Project or Update All Design Points to start a local run of the simulation

Figure 26


The evaluated curves can be shown also inside the parameter manager with inserted charts:

Insert Charts

Choose Angle for the x axis definition

Choose Ang_Back for y axis 1 and Ang_Fwd for y axis 2

Abbildung 27

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HANDS on Position Sensor Introduction to ANSYS Maxwell PRACE 2013